Episomal maintenance of S/MAR-containing non-viral vectors for RPE-based diseases.

The efficacy of non-viral genetic therapies has historically been limited by transient gene expression and vector loss. Scaffold matrix attachment regions (S/MARs) have been shown to augment transcription, promote episomal maintenance, and provide insulator-like function to DNA in in vitro and in vivo systems. Here we explore the ability of S/MAR elements to mediate these effects in retinal pigment epithelial (RPE) cells with the eventual goal of improving the persistence of expression of our non-viral gene delivery tools. We engineered an RPE-specific reporter vector with or without an S/MAR immediately downstream of the eGFP expression cassette. We show that the S/MAR vector is maintained as an episome for up to 1 year. Experiments in which rhodamine-labeled DNA was delivered to the subretinal space of mice show better persistence of the S/MAR-containing vector in the RPE than the non-S/MAR vector. These results suggest that inclusion of the S/MAR region promotes episomal maintenance of plasmid DNA in the RPE after subretinal delivery and that inclusion of this DNA element may be beneficial for non-viral ocular gene transfer.